This paper reports a molecular-dynamics study on the clustering of ${\text{Eu}}^{3+}$ ions incorporated in ${\text{SiO}}_2$ glass. Classical molecular-dynamics experiments were carried out on $x{\text{Eu}}_2{\text{O}}_3\text{−}\left(100-x\right){\text{SiO}}_2$ ($x=0$, 1, 2, 3, 4, and $5\text{mol}\%$) glasses using empirical pairwise Morse interatomic potentials. Due to statistically improved simulation results, averaged over hundreds of ${\text{Eu}}^{3+}$ ions, the effects of ${\text{Eu}}_2{\text{O}}_3$ content on the silica network, ${\text{Eu}}^{3+}$ coordination, and on ${\text{Eu}}^{3+}$ clustering were properly analyzed. At $1\text{mol}\%$ ${\text{Eu}}_2{\text{O}}_3$ most $\left(\sim 70\%\right)$ of ${\text{Eu}}^{3+}$ ions are isolated in silica host but have a strained coordination with typically three short bonds to nonbridging oxygens plus one long bond to bridging oxygen. It is found that the ${\text{Eu}}^{3+}\text{-O}$ coordination number increases from 4.5 to 4.9 atoms due to an increase in sharing of nonbridging oxygens. This follows an increase in the ${\text{Eu}}^{3+}{\text{-Eu}}^{3+}$ coordination number due to an increasing clustering of ${\text{Eu}}^{3+}$ ions. ${\text{Eu}}^{3+}$ clustering is already present in the sample with $1\text{mol}\%$ ${\text{Eu}}_2{\text{O}}_3$, but most of the clustered ${\text{Eu}}^{3+}$ ions are present only in pairs. As ${\text{Eu}}_2{\text{O}}_3$ content increases in the glass, both the proportion of ${\text{Eu}}^{3+}$ ions involved in clusters and the size of individual clusters increase, and signs of phase separation become apparent for $5\text{mol}\%$ ${\text{Eu}}_2{\text{O}}_3$.

• Received 18 September 2008

DOI:https://doi.org/10.1103/PhysRevB.79.024202